Macrocyclic compounds having olfactory properties similar to the natural musks and processes for their preparation are known. The process most commonly used and presently considered to be the only acceptable method for the commercial preparation of these macrocyclic compounds is the depolymerization of linear polyesters accompanied by ring closure to form the macrocycle.
U.S. Pat. No. 2,092,031 discloses a process for the preparation of cyclic esters having more than seven atoms in the ring via depolymerization of the corresponding linear polyester by heating the polyester under vacuum in the presence of a metal catalyst. Similar processes have also been described in British Pat. No. 1,108,720, U.S. Pat. No. 3,431,279, Czech Pat. No. 108,762 and by E. W. Spanagel et al. in J. Am. Chem. Soc., 57, 929,934 (1935).
While these thermal depolymerization processes are extremely useful, there are certain problems associated with their use. Most of these problems are the result of the highly viscous reaction mass and the difficulty in achieving good heat transfer within such a mass. Even when operating the process as a batch-type operation with a relatively small unit charge or when operating in a continuous or semi-continuous manner with efficient agitation, such as described in U.S. Pat. No. 4,165,321, some thermal decomposition will result. The thermal decomposition products not only discolor the resulting product but also impart a characteristic "amber" odor. The nature of these malodorous bodies is not known, however, their presence in the finished product is objectionable to perfumers even when present in trace amounts which are not easily detected or identified with sophisticated instrumentation or by analysis. The malodorous constituents cannot be completely removed by distillation and treatment with charcoal, activated carbon or clays, while significantly improving the color of the product, will not completely eliminate these undesirable odor bodies.
It would be highly desirable if a process were available for the removal of such malodorous components which detract from or mask the desired olfactory properties of the macrocyclic fragrance compound. It would be even more advantageous if such a process were adaptable to commercial operation and, in addition to enhancing the olfactory properties, if other benefits such as improving the color, thermal stability, etc. of the finished product could be obtained.